As the use of digital data increases, the demand for faster, smaller, and more efficient memory structures increases. One type of memory structure that has recently been developed is a crossbar memory array. A crossbar memory array includes a first set of conductive lines which intersect a second set of parallel conductive lines. Programmable memory elements configured to store digital data are placed at intersections between the first set of lines and second set of lines.
One type of memory element which can be used is a memristive memory element. A memristive memory element can change the state of its resistance in response to an applied electrical condition such as a voltage or an electric current. The resistive state of a memristive memory element can be used to store digital data. For example, a high resistance state can represent a digital ‘0’ and a low resistance state can represent a digital ‘1’.
The electrical conditions used to set the state of a memristive memory element are typically applied in an open loop configuration. This means that the circuitry applying the electrical conditions is not made aware of the resistive state of the memristive devices being set. This leads to a variation in resistance levels between memristive memory elements in a particular state. It can also lead to a variation in resistance levels of one memory element in a particular state after each set. For example, all of the memristive memory elements in a memory array that are set to a high resistive state may have varying resistance levels. Additionally, all of the memristive memory elements in the array set to a low resistive state may have varying resistance levels. Furthermore, a selected memory element set to a high resistance level may have varying resistance levels after each write operation. This can cause issues with the performance of the memory array including, but not limited to, increased error rate in memory reading, and reduced upper limit of write cycles.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.